A hybrid vehicle may selectively enter and exit a regeneration mode or regenerative braking where the vehicle's kinetic energy is converted to electrical energy and stored for later use. The vehicle may enter regeneration mode during times when driver demand is low, such as when the hybrid vehicle is traveling down a road that has a negative grade. An electric machine provides a negative torque to the hybrid vehicles powertrain during regeneration. The negative torque helps to provide vehicle braking, but vehicle braking may also be provided by friction brakes. If negative torque provided by the electric machine is not applied to the vehicle's wheels due to transmission degradation, the vehicle may not decelerate at a desired rate. Further, there may be a delay that is longer than may be desired to increase braking force applied by friction brakes to provide a desired amount of vehicle braking.
The inventors herein have recognized the above-mentioned issues and have developed a powertrain operating method, comprising: predicting a transmission input shaft speed from a transmission output shaft speed; and adjusting an actuator in response to an actual transmission input shaft speed minus the predicted transmission input shaft speed.
By predicting a transmission input speed based on a transmission output speed, it may be possible to provide the technical result of determining transmission degradation so that automatic friction braking may be initiated sooner. Further, it may be possible to reduce negative torque applied to a transmission input shaft sooner so that transmission input shaft speed may be maintained above a threshold speed above which a transmission pump provides a desired amount of transmission fluid flow or pressure.
The present description may provide several advantages. Specifically, the approach may provide improved vehicle performance during conditions of transmission degradation. In addition, the approach may improve vehicle braking during conditions of transmission degradation. Further, the approach may reduce an amount of time taken to determine degradation so that control actions may be performed sooner.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.